1. Field of the Invention
The disclosures herein generally relate to an actuator element, a liquid drop discharge head, a liquid drop discharge apparatus and an image forming apparatus, and especially relate to an actuator element including an electromechanical conversion element or an electrothermal conversion element, a liquid drop discharge head including the actuator element, a liquid drop discharge apparatus and an image forming apparatus respectively including the liquid drop discharge head.
2. Description of the Related Art
Some liquid drop discharge heads include a nozzle that discharges liquid drops, a liquid chamber which is in communication with the nozzle and an actuator including an electromechanical conversion element, such as a piezoelectric element, for applying pressure on a liquid in the liquid chamber or an electrothermal conversion element, such as a heater. The actuator element is formed by laminating various thin films, such as an electrode film or a piezoelectric film on a substrate. For example, a piezoelectric element as an electromechanical conversion element has a laminated constitution in which a lower electrode film is formed on a substrate, a piezoelectric film is formed on the lower electrode film, and an upper electrode film formed on the piezoelectric film. For a characteristic of the electrode films, which are formed on both sides of the piezoelectric film, a function on an aspect of the piezoelectric characteristic of the piezoelectric film and a material characteristic to ensure crystallinity and a function on an aspect of an electrical characteristic to transmit a drive signal from an external circuit to the piezoelectric film are required. In order to have the above two functions, the electrode film may be formed to have a laminated structure including two or three layers.
Japanese Published Patent Application No. H11-077999 discloses a recording head of ink-jet type, in which a conductive film (wiring) includes a contact part (through hole for connection) in a plane and runs to side walls of a liquid chamber at least in two directions. In the recording head, when a pattern of the conductive film is formed, stress is received by plural side walls, and stress on a piezoelectric film around the contact part is reduced. Accordingly, an occurrence of a crack or a break in the piezoelectric film due to the stress concentration at the contact part is prevented.
However, in the recording head disclosed by Japanese Published Patent Application No. H11-077999, when a wiring is formed via the through hole for connection in an insulation film formed on an electrode film after the electrode film is formed, interfacial peeling may occur, i.e. the electrode film peels around the through hole for connection in the electrode film. In the case where the electrode film is formed by laminating plural layers, the interfacial peeling may occur between the uppermost layer film, which faces the through hole for connection, and a lower layer film adjacent to the uppermost layer film.
Japanese Published Patent Application H11-077999 discloses a configuration which prevents an occurrence of a crack or a break in the piezoelectric film, but does not describe the problem of the interfacial peeling around the through hole for connection of the electrode film or a configuration to solve the problem.